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Dự báo khả năng tiêu hóa cỏ của động vật nhai lại bằng phương pháp enzym
Prediction of digestibility of North Vietnamese grasses for ruminant by the enzymatic method with "persine-cellulase" of De Boever: first results Paul Pozy, Vu Chi Cuong, Doan Thi Khang and Daniel Dehareng 1. Introduction The digestibility of feed for ruminants is classically determined by measuring the quantity ingested and the faecal matter excreted by animals. However, even with sheep this method is long and laborious. It is for that reason that laboratory methods (in vitro) were developed to predict digestibility in vivo, and on that basis determine the energetic value of feedstuffs. Among these methods, one technique based on the use of "pepsine" and "cellulase", developed in Europe by De Boever (1986) is often used. Recently, this method was introduced in NIAH's chemical analysis laboratory. The present study follows two objectives. First to see that De Boever's method has been correctly transferred to NIAH. If that proves to be so, then determine the precision of the predictability of in vivo digestibility based on in vitro measures according to De Boever's method. 2. Meterials and methods Following practical and theoretical training of Vietnamese staff in Louvain's laboratory of animal physiology in Belgiun, the method was introduced in NIAH in such away that techniques, equipment and enzymatic products were identical in both laboratories. Reference samples of tropical and temperate origins, whose in vitro digestibility had been previously been determined by De Boever's labotatoty, were sent to Hnoi to calibrate the method. Indeed, the method to determine in labotatoty the digestibility of organic matter (in vitro) is an indirect method; it requires a correction (a calibration) of the parameters measured with reference to standard samples of known digestibility. In this study, all the fodder studies were harvested under the practical conditions of dairy farms around Hanoi. Part of them was subjected to in vitro measures of digesbitility in UCL and in Hanoi (1 st objective of the study; many sample from 3 harvests of narural grasses made in April, June and August 1999). Another part was subjected in Hanoi to in vitro digestibility measures (on sheep) and in vitro, to determine intensity of the relation linking the two types of measures, that is to evaluate the predictability of digestibility in vivo from in vitro measures of digestibility (2 nd objective). In this case, the correlation analysis has focused, for practical purposes, on two groups of feed: narural glasses harvested for 5 experiences in vivo throughout one year (17 pairs of measures) and cultivated grasses (Pennisetum Purpurum, Tripsacum laxum, maize) including rice straw (21 pairs and 7 experiences in vivo). 3. Results The comparison of digestibility values in vitro (IVD MO ) measures in UCL and Hanoi (Table 1) on samples of narural grasses harvested in April (HNO4), June (HNO6) and August (HNO8) shows that the difference is less than 2.5%, less than the error generally allowed for the manipulations. The method is operational in NIAH's labotatory. Grass Digestibility in vitro (IVD MO ) MS MO UCL Lab. NIAH Lab. HNO4 49.7 88.1 57.64 57.60 56.97 56.13 55.73 56.27 58.20 HNO6 27.7 86.8 63.75 64.72 63.24 68.18 67.14 63.22 HNO8 32.3 85.1 57.46 57.35 55.51 55.81 58.89 55.35 T-test = 0.4888 with 2 degrees of freedom Morever, the analysis of correlations has shown that a weak relation (P<0.01) (R 2 =0.442) between the coefficient of digestive utilisation of the natural grasses compiled from the in vivo method (CUD MO ) and its comparative value from the in vitro method (IVD MO ): Y (CUD MO ) = 0.7807*X (IVD MO ) + 14.3953 avec r = 0.6645** In contrast, the relation (P<0.01) between the two digestive utilisation coefficient is fairly strong (R 2 = 0.807) in the case of cultivated grasses: Y (CUD MO ) = 0.7778 * X(IVD MO ) + 21.7623 avec r = 0.8985** This difference in the strength of correlations established for the two groups of feed, and therefore the precision of the predictability of the in vivo digestibility from in vitro measures, probably comes from the greater variability in the chemical composition (MO, NDF, MAT) of natural grasses than in cultivated grasses. Nevertheless, at this stage of use of the in vitro method, we can reasonably state that in practice, the precision of the prediction is sufficient only for use in the formulation of more accurate food rations. 4. Conclusions The transfer of the De Bowver method has been successful and NIAH has now a quick and performing method to predict the energetic value of feed for dairy cows from the knowledge of the digestibility of their organic matter. However, the continuation of the study of other feeds by the in vivo nad in vitro methods, but the accumulation of digestibility data, will permit the consolidation of the established correlations. Acknowlegements Thanks to the UCL lab. The Vietnamese and Belgian goverments financed this study. Summary A study was undertaken to establish the possible correlations between in vivo and in vitro digestibility of ruminat feeds . Parallelly, a series of in vivo digestibility trials with sheep and in vitro digestibility experiments using pepcine- cellulase technique developed by De Bover (1986) in Belgium was conducted. It revealed that: The difference in digestibility values in vitro (IVD MO ) measures in UCL and Hanoi on samples of narural grasses was less than 2.5% (accepted error), less than the error generally allowed for the manipulations. The method is operational in NIAH's labotatory. The is a weak relation (P<0.01) (R 2 =0.442) between the coefficient of digestibility of the natural grasses from the in vivo method (CUD MO ) and its comparative value from the in vitro method (IVD MO ): Y (CUD MO ) = 0.7807*X (IVD MO ) + 14.3953 avec r = 0.6645** In contrast, the relation (P<0.01) between the two coefficients of digestibility coefficient is fairly strong (R 2 = 0.807) in the case of cultivated grasses: Y (CUD MO ) = 0.7778 * X(IVD MO ) + 21.7623 avec r = 0.8985** . Prediction of digestibility of North Vietnamese grasses for ruminant by the enzymatic method with "persine-cellulase" of De Boever: first results Paul Pozy, Vu. physiology in Belgiun, the method was introduced in NIAH in such away that techniques, equipment and enzymatic products were identical in both laboratories. Reference samples of tropical and temperate